Physics and Measurement

Transcription

1 Name Class Date Skills Practice Lab Physics and Measurement DATASHEET FOR IN-TEXT LAB In this laboratory exercise, you will gain experience making measurements as a physicist does. All measurements will be made using units to the precision allowed by your instruments. OBJECTIVES Measure accurately using typical laboratory equipment. Measure length and mass in SI units. Determine the appropriate number of significant figures for various measurements and calculations. Examine the relationships between measured physical quantities by using graphs and data analysis. MATERIALS LIST 2 rectangular wooden blocks 15 cm metric ruler balance meterstick rectangular wooden block stopwatch SAFETY Perform this lab in a clear area. Falling or dropped masses can cause serious injury. Procedure PREPARATION 1. Read the entire lab procedure, and plan the steps you will take. MEASURING LENGTH, WIDTH, THICKNESS, AND MASS 2. Record your data for steps 3 7 in the data table below. Length (cm) Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 Trial 6 Width (cm) Thickness (cm) Mass (kg) Copyright by Holt, Rinehart and Winston. All rights reserved. Holt Physics 1 The Science of Physics

2 Name Class Date Physics and Measurement continued 3. Use a meterstick to measure the length of the wooden block. Record all measured digits plus one estimated digit. 4. Follow the same procedure to measure the width and thickness of the block. Repeat all measurements two more times. Record your data. 5. Carefully adjust the balance to obtain an average zero reading when there is no mass on it. Your teacher will show you how to adjust the balances in your classroom to obtain an average zero reading. Use the balance to find the mass of the block. Record the measurement in your data table. 6. Repeat the mass measurement two more times, and record the values in your data table. Each time, move the block so that it rests on a different side. 7. For trials 4 6, repeat steps 3 through 6 with the second wooden block. MEASURING TIME AND DISTANCE 8. Record your data for steps 9 13 in the data table below. Trial Distance Time (s) Copyright by Holt, Rinehart and Winston. All rights reserved. Holt Physics 2 The Science of Physics

3 Name Class Date Physics and Measurement continued 9. Perform this exercise with a partner. One partner will drop the wooden block from a measured height, and the other partner will measure the time it takes the block to fall to the floor. Perform this in a clear area away from other groups. 10. One student should hold the wooden block straight out in front of him or her at shoulder height. Hold the block between your hands. Use the meterstick to measure the height to which the wooden block is raised. Record this distance in your data table. 11. Use the stopwatch to time the fall of the block. Make sure the area is clear, and inform nearby groups that you are about to begin. The student holding the block should release it by pulling both hands straight out to the sides. The student with the stopwatch should begin timing the instant the block is released and stop timing as soon as the block hits the floor. In your data table, record the time required for the block to fall. 12. Repeat for two more trials, recording all data in your data table. Try to drop the block from exactly the same height each time. 13. Switch roles, and repeat steps 10 through 12. Perform three trials. Record all data in your data table. Analysis 1. Organizing Data Using your data from the first data table, calculate the volume of the wooden block for each trial. The equation for the volume of a rectangular block is volume length width thickness. 2. Analyzing Data Use your data from the first table and your results from item 1 above to answer the following questions. a. For each block, what is the difference between the smallest length measurement and the largest length measurement? Copyright by Holt, Rinehart and Winston. All rights reserved. Holt Physics 3 The Science of Physics

4 Name Class Date Physics and Measurement continued b. For each block, what is the difference between the smallest calculated volume and the largest calculated volume? c. Based on your answers to (a) and (b), how does multiplying several length measurements together to find the volume affect the precision of the result? 3. Analyzing Data Did the block always fall from the same height in the same amount of time? Explain how you found the answer to this question. 4. Constructing Graphs Using the data from all trials, make a scatter plot of the distance versus the time of the block s fall. Use a graphing calculator, computer, or graph paper. Conclusions 5. Drawing Conclusions For each trial in the first data table, find the ratio between the mass and the volume. Based on your data, what is the relationship between the mass and volume? Copyright by Holt, Rinehart and Winston. All rights reserved. Holt Physics 4 The Science of Physics

5 Name Class Date Physics and Measurement continued 6. Evaluating Methods For each type of measurement you made, explain how error could have affected your results. Consider method error and instrument error. How could you find out whether error had a significant effect on your results for each part of the lab? Explain the role of human reaction time in your measurements. Extension 7. Evaluating Data If there is time and your teacher approves, conduct the following experiment. Have one student drop the wooden block from shoulder height while all other class members time the fall. Perform three trials. Compare results each time. What does this exercise suggest about accuracy and precision in the laboratory? Copyright by Holt, Rinehart and Winston. All rights reserved. Holt Physics 5 The Science of Physics

6 CHAPTER 1 Skills Practice Lab Lab Planning Beginning on page T34 are preparation notes and teaching tips to assist you in planning. Blank data tables (as well as some sample data) appear on the One-Stop Planner. No Books in the Lab? See the Datasheets for In-Text Labs workbook for a reproducible master copy of this experiment. CBL Option A CBL version of this lab appears in the CBL Experiments workbook. Safety Caution Remind students to be aware of other groups activities. Falling objects can cause serious injury. CHAPTER 1 Skills Practice Lab OBJECTIVES Measure accurately using typical laboratory equipment. Measure length and mass in SI units. Determine the appropriate number of significant figures for various measurements and calculations. Examine the relationships between measured physical quantities by using graphs and data analysis. MATERIALS LIST 2 rectangular wooden blocks 15 cm metric ruler balance meterstick rectangular wooden block stopwatch In this laboratory exercise, you will gain experience making measurements as a physicist does. All measurements will be made using units to the precision allowed by your instruments. SAFETY PROCEDURE Preparation Physics and Measurement Perform this lab in a clear area. Falling or dropped masses can cause serious injury. 1. Read the entire lab procedure, and plan the steps you will take. Measuring Length, Width, Thickness, and Mass 2. If you are not using a datasheet provided by your teacher, prepare a data table in your lab notebook with seven columns and five rows, as shown below. In the first row, label the second through seventh columns Trial 1, Trial 2, Trial 3, Trial 4, Trial 5, and Trial 6. In the first column, label the second through fifth rows Length (cm), Width (cm), Thickness (cm), and Mass (kg). Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 Trial 6 Length (cm) Width (cm) Thickness (cm) Mass (kg) Chapter 1

7 3. Use a meterstick to measure the length of the wooden block. Record all measured digits plus one estimated digit. 4. Follow the same procedure to measure the width and thickness of the block. Repeat all measurements two more times. Record your data. 5. Carefully adjust the balance to obtain an average zero reading when there is no mass on it. Your teacher will show you how to adjust the balances in your classroom to obtain an average zero reading. Use the balance to find the mass of the block, as shown in Figure 1. Record the measurement in your data table. 6. Repeat the mass measurement two more times, and record the values in your data table. Each time, move the block so that it rests on a different side. 7. For trials 4 6, repeat steps 3 through 6 with the second wooden block. Measuring Time and Distance 8. If you are not using a datasheet provided by your teacher, prepare a second data table in your lab notebook with three columns and seven rows, as shown below. In the first row, label the columns Trial, Distance (m), and Time (s). Label the second through seventh rows 1, 2, 3, 4, 5, and 6. Trial Distance (m) Time (s) Figure 1 Step 3: Always record measurements to the precision allowed by your instruments. Step 5: Make sure you know how to use the balances in your classroom. The balance should read zero when there is no mass on it. The number of significant figures in your measurement will be determined by your instrument, the object being measured, and the purpose of your measurement. The Science of Physics 35 CHAPTER 1 LAB Tips and Tricks Remind students to record all measured digits plus one estimated digit. Students may repeat all length measurements using the 15 cm ruler. Students should practice timing the falling block before recording falling-block data. Better results that are easier to reproduce will be obtained with a greater falling distance. Show students the proper way to hold a meterstick when taking a measurement. Show students how to adjust the balances to zero. If you are using triple-beam balances, demonstrate handling the balances and moving the masses to take a measurement. Demonstrate how to hold the block between your hands and release the block by pulling your hands straight out to the sides. Show how this method prevents the block from turning, whereas other methods cause the block to turn. Make sure students know how to operate and read a stopwatch. Checkpoints Step 3: Make sure all students perform all measurements. Students should be able to explain how they assign significant figures to their measurements. Step 5: Students may need help using the balance for the first time. For some balances, instrument drift may prevent a continuous zero reading, so an average zero reading will be the goal. 35

8 CHAPTER 1 LAB Step 10: Students should hold the block at about shoulder height for each trial. In step 13, the second student should hold the block at his or her own shoulder height. Step 11: Before recording data, students should practice until they can demonstrate that the timer starts at the moment the block is released and stops when the block hits the floor. ANSWERS Analysis 1. Answers will vary, depending on the blocks used. Make sure answers have the right number of significant figures. For sample data, block 1 Trial 1 has a volume of cm Answers will vary. a. For the sample data block 1, the answer is 8.15 cm. b. For the sample data block 1, the answer is 14 cm 3. c. Students should recognize that the answer becomes less precise as several values are multiplied and that the difference between the highest and lowest answers becomes greater. 3. Student answers should state that the block always falls from the same height in the same amount of time. If students answer the question by finding the ratio between distance and time, they will find different values for different heights. 4. The graph should show one point for each height from which the block fell. 36 Figure 2 Step 10: Hold the block between your hands. Step 11: Release the block by pulling both hands straight out to the sides. It may take some practice to release the block so that it falls straight down without turning. 36 Chapter 1 9. Perform this exercise with a partner. One partner will drop the wooden block from a measured height, and the other partner will measure the time it takes the block to fall to the floor. Perform this in a clear area away from other groups. 10. One student should hold the wooden block straight out in front of him or her at shoulder height. Hold the block between your hands, as shown in Figure 2. Use the meterstick to measure the height to which the wooden block is raised. Record this distance in your data table. 11. Use the stopwatch to time the fall of the block. Make sure the area is clear, and inform nearby groups that you are about to begin. The student holding the block should release it by pulling both hands straight out to the sides. The student with the stopwatch should begin timing the instant the block is released and stop timing as soon as the block hits the floor. In your data table, record the time required for the block to fall. 12. Repeat for two more trials, recording all data in your data table. Try to drop the block from exactly the same height each time. 13. Switch roles, and repeat steps 10 through 12. Perform three trials. Record all data in your data table.

9 ANALYSIS 1. Organizing Data Using your data from the first data table, calculate the volume of the wooden block for each trial. The equation for the volume of a rectangular block is volume = length width thickness. 2. Analyzing Data Use your data from the first table and your results from item 1 above to answer the following questions. a. For each block, what is the difference between the smallest length measurement and the largest length measurement? b. For each block, what is the difference between the smallest calculated volume and the largest calculated volume? c. Based on your answers to (a) and (b), how does multiplying several length measurements together to find the volume affect the precision of the result? 3. Analyzing Data Did the block always fall from the same height in the same amount of time? Explain how you found the answer to this question. 4. Constructing Graphs Using the data from all trials, make a scatter plot of the distance versus the time of the block s fall. Use a graphing calculator, computer, or graph paper. CONCLUSIONS CHAPTER 1 LAB Conclusions 5. Answers should state that both wooden blocks have the same mass-to-volume ratio, even though their masses and volumes are not the same. Some students may realize that this value is that of the density of the wood. 6. Student answers will vary but should include an analysis of error in the laboratory. Students should understand that reaction time is part of the error in the block experiment. Extension 7. Typically, a range of values is reported as different class members measure the time of the same event. This result should lead students to realize that for short times, error can be a significant factor. 5. Drawing Conclusions For each trial in the first data table, find the ratio between the mass and the volume. Based on your data, what is the relationship between the mass and volume? 6. Evaluating Methods For each type of measurement you made, explain how error could have affected your results. Consider method error and instrument error. How could you find out whether error had a significant effect on your results for each part of the lab? Explain the role of human reaction time in your measurements. EXTENSION 7. Evaluating Data If there is time and your teacher approves, conduct the following experiment. Have one student drop the wooden block from shoulder height while all other class members time the fall. Perform three trials. Compare results each time. What does this exercise suggest about accuracy and precision in the laboratory? The Science of Physics 37 37

10 The Holt Physics Lab Program T34 Lab Procedures Introduction Holt Physics offers you and your students several options for classroom labs. Each chapter in the textbook is followed by a full-scale laboratory investigation either a Skills Practice Lab or an Inquiry Lab. Skills Practice Labs are investigations of physics principles in a traditional, multi-step format. In contrast, Inquiry Labs provide students with a predetermined set of materials and a stated goal and challenge students to design an experiment to satisfy the goal. The workbook Datasheets for In-Text Labs contains reproducible masters of the complete procedure for each lab. These datasheets provide space for students to record their data and answers. This workbook also contains a Skills Practice version of each textbook-based Inquiry Lab. The fully-articulated steps in these versions offer you the option to use a more traditional approach. Appendix K in this textbook contains some end-of-chapter labs modified for use with CBL 2 equipment. The workbook CBL Experiments contains reproducible masters of the complete procedure for each lab in Appendix K. It also contains CBL 2- modified versions of some end-of-chapter labs and extra, scenariobased CBL 2 labs that correspond to most book chapters. Alternate versions of the labs using first-generation CBL (rather than CBL 2) equipment can be found at go.hrw.com. The textbook also contains many Quick Labs, which are brief demonstrations that require few materials. Some Quick Labs are appropriate as homework assignments and are designated as such in the Teacher Edition. A separate Laboratory Experiments workbook contains two types of additional full-scale labs. Discovery Labs allow students to explore physics phenomena before they study the corresponding chapter. Invention Labs are open-ended inquiry-based labs couched in terms of an engaging, real-world scenario. Students are challenged to test a material or invent a device to solve a specific problem. In lieu of a traditional lab report, students submit a patent application for their invention or process. The following pages contain preparation notes and teaching tips for the chapter labs and Appendix K labs found in this textbook. Teaching Tips for Inquiry Labs Prior to starting an Inquiry Lab, each student or group should turn in a detailed procedure for approval. You may wish to start this process a few days before the lab period, to allow yourself time to review the procedures and to allow the students time to make necessary revisions. Compare student procedures to the Sample Procedures found on the following pages. Use the Checkpoints following each sample procedure as guidelines for things to look for in the procedures and to identify areas where students may need extra help when carrying out the procedures in the lab. Students may use a procedure that differs from the sample procedure only if the alternate procedure meets the following conditions: The procedure is safe. The procedure can be done in the allotted time. All necessary materials are available. The procedure will prepare the students to answer the questions at the end of the lab when they are finished. Before starting the procedure, students should revise their procedures according to your comments. You may want to look over revised procedures before granting final approval. Evaluate student procedures according to organization, clarity, completeness, safety, how well they follow the steps of the scientific method, and how well they prepare students to answer the questions at the end of the lab. Return procedures with your comments to students before they begin the lab.

11 Additional Support for In-Text Labs Ch.1 Skills Practice Lab: Physics and Measurement Planning Recommended time: 1 2 lab periods Classroom organization: Each lab group should have two students. Students should alternate duties so that each student performs all steps. For the second part of the lab, each group needs a large, clear area to work in. If possible, consider conducting this part of the lab in a large, open space, such as outdoors or in a gymnasium. Materials (for each lab group) 3 wooden blocks alarm stopwatch, 12- or 24-hour balance: portable, electronic balance or triple-beam balance with weight meterstick metric ruler, 15 cm long Required Precautions: Wear eye protection and other required safety equipment when cutting wood blocks. Follow all instructions and safety guidelines for the equipment. Do not work with power tools without other people present. Materials Preparation: The wood blocks should be cut from standard 2 in. by 4 in. lumber. For future labs, each lab group should have 4 blocks, cut into lengths of approximately 10 cm, 15 cm, 20 cm, and 25 cm. Ch.2 Skills Practice Lab: Free-Fall Acceleration Planning Recommended time: 1 lab period Calibrating the recording timer may be done separately, or it may be skipped entirely if the period of the timer is known. Classroom organization: Each lab group should have two students. Each group needs a level work surface at least 0.5 m above the floor with an edge to clamp the stand base onto. Each group needs clear floor space of at least 1.0 m 2. For the recording timer calibration, each group needs enough open space so the student can walk away from the timer in a straight line for 3.0 s. Materials (for each lab group) 1-position support base and rod, 1.3 cm 91 cm balance: portable, electronic balance or triple-beam balance with weight C-clamp meterstick Additional Materials (for chapter lab) alarm stopwatch, 12- or 24-hour metric hooked mass set recording timer: acceleration timer, tabletop acceleration timer, or compact spark timer replacement paper tape, 13 mm replacement carbon disks Additional Materials (for Appendix K lab) 3 wooden blocks of different masses LabPro or CBL 2 interface roll of masking tape thin foam pad TI graphing calculator with link cable V-clamp Vernier motion detector Required Precautions: Wear eye protection and other required safety equipment when cutting wood blocks. Follow all instructions and safety guidelines for the equipment. Do not work with power tools without other people present. Materials Preparation: The wood blocks for the Appendix K procedure should be cut from standard 2 in. by 4 in. lumber. Each lab group should have 4 blocks cut into lengths of approximately 10 cm, 15 cm, 20 cm, and 25 cm. Ch.3 Inquiry Lab: Velocity of a Projectile Planning Recommended time: 1 lab period Classroom organization: Each group must have at least two students. Each group needs a level surface at least 0.5 m above the floor, with at least 2.0 m of space in front of the surface. Materials (for each lab group) 1-position support base and rod, 1.3 cm 91 cm aluminum sheet, 12.5 cm 25 cm, in. thick C-clamp carbon paper, 4 sheets cardboard box inclined plane meterstick right-angle clamp for 1.3 cm rods roll of black nylon cord roll of adhesive packing tape roll of adhesive tape, 0.5 in. wide roll of masking tape Lab Procedures T35